Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $204.52   13.581%   $232.2959   $232.30   $232.30   $232.30  
  Purchase #2 $66.53   3.210%   $68.6656   $68.67   $68.65   $68.70  
  Purchase #3 $24.60   4.734%   $25.7646   $25.76   $25.75   $25.80  
  Purchase #4 $39.47   11.316%   $43.9364   $43.94   $43.95   $43.90  
  Purchase #5 $234.86   3.485%   $243.0449   $243.04   $243.05   $243.00  
  Purchase #6 $89.54   6.621%   $95.4684   $95.47   $95.45   $95.50  
  Purchase #7 $24.98   5.541%   $26.3641   $26.36   $26.35   $26.40  
  7 purchase totals = $684.50       $735.5399   $735.54   $735.50   $735.60